The manufacture and repair of screens extending about the lower periphery of the main cylinder of a carding machine is a time consuming procedure requiring the talents of skilled craftsmen. The screen extends about 40 to 45 inches across the carding machine parallel with the axis of the main cylinder and the combined length of the front and rear portions of the card screen ranges from 50 to 64 inches. Each of the front and rear sections are formed in an arc when viewed from the side and the two sections include means for connecting them together beneath the axis of the main cylinder in conforming relation to the curvature of the main cylinder. The card screen comprising the front and rear sections is spaced a predetermined distance measured in thousandths of an inch from the lower periphery of the main cyclinder. As the main cyclinder rotates at speeds approximating thirty five to fifty miles per hour trash and non-spinable fibers are thrown from the lap and passed through the air space between adjacent grid bars in the card screen.
The front and back screens each comprise side ribs extending along opposite sides of the screen and transverse blanks extending between the side ribs adjacent the doffer and the lickerin. End bars are provided in the proximal ends of the front and rear screen portions adjacent their juncture beneath the axis of the main cylinder. The end bars are formed of sturdy stock to effectively brace and strengthen the screen at its center. A plurality of grid bars extend transversely of the screen in parallel relation to the end bars. The grid bars are spaced from each other a predetermined distance longitudinally of the screen and the number of grid bars varies from screen to screen and is dependent on the length of the screen the width and spacing of the bars and the air space between adjacent bars. There may be as many as 82 bars in a card screen. Each of these bars, according to the prior art, is soldered to the side ribs and to a central rib, if one is provided. The grid bars may be spaced from each other along the length of the card screen about 3/16s of an inch and there is an approximate equal spacing between the grid bars and the proximate blank and end bar.
It is important to satisfactory carding that the spacing be uniform and this requirement of careful spacing and the need for skilled soldering of each rib causes the manufacture and repair of card screens to be a time consuming process requiring the services of skilled craftsmen. Another factor contributing to the time and skill required in the conventional manufacture and repair of card screens is the need to straighten the screen to it's predetermined configuration after the screen has been distorted by heat from the soldering operation. The completed screen must have a smooth surface in order to prevent tagging by the fibers as they pass the screen and this need for a smooth surface requires the removal of excess solder by grinding and polishing, thereby adding to the time and skill required in the manufacture and repair of screens for carding machines. The extensive use made of solder in the manufacture and repair of card screens according to the prior art undesirably exposes the workers to lead molecules which are hazardous to the worker's health.
Card screens frequently require repair because a "choke" or large clump of fibers passes between the main cyclinder and the card screen. The resulting pressure frequently causes some of the grid bars to become bent and/or disconnected from the supporting side ribs and, if provided, the central rib. Because of the skill required in assembling the components of a card screen to the close tolerances needed for effective carding the damaged screens are generally returned to the same skilled craftsmen who manufactured the original screen. Repair is accomplished by the same time consuming alignment, soldering, straightening and polishing techniques as were required in the initial manufacture of the screen.